Dengue vaccine is just a year away, researchers say

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The vaccine seems to be more effective for three dengue types and older children

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[KUALA LUMPUR] A new vaccine that can halve the number of dengue cases provides a welcome shot to fight a deadly disease that infects around 390 million people every year in the tropics.

Sanofi Pasteur, the pharmaceutical company that sponsored the development of the vaccine, has announced that it will be commercially available by July 2015.

At present, no licensed vaccine is available to prevent dengue, a mosquito-borne disease. This is the first dengue vaccine to reach phase 3 trial, the last stage of clinical testing, according to a study in the British medical journal The Lancet (11 July).

The phase 3 trial was conducted in South-East Asia that accounts for 70 per cent of the global dengue burden. The results showed an overall vaccine efficacy with a 56 per cent reduction of dengue fever incidence, and 80 per cent reduction of serious cases. The vaccine is also safe to use as recipients did not suffer from any vaccine-related health complications, the results showed.

The trial covered 10,275 children aged 2-14 years in Indonesia, Malaysia, the Philippines, Thailand and Vietnam. The children were randomly assigned to receive either the vaccine or a placebo of saline solution. They received three doses of the vaccine or placebo on months 0, 6 and 12, and were monitored until month 25.

“Weekly calls were made to the parents to determine the children’s well-being,” says Revathy Nallusamy, co-author of the study and a paediatrician who coordinated the trial at Penang, Malaysia. If a child experienced high fever, doctors would check the child’s blood for dengue virus.

Scientists created the vaccine by inserting surface proteins of dengue virus into a backbone of yellow fever virus non-structural proteins. “The vaccine will trigger an immune response in vaccinated individuals without causing the disease,” says Shamala Devi, medical immunologist at University of Malaya in Malaysia. “This allows the immunity system to stage an early defence against future dengue virus infections.”

Annelies Wilder-Smith, a professor at Lee Kong Chian School of Medicine, Singapore, who led an earlier phase 2 trial of the same vaccine among adults in that country, views the last-stage trial results with guarded optimism. “It looks like a promising vaccine, but it is not perfect,” she tells SciDev.Net.

Dengue is caused by a virus with four serotypes. But the new vaccine is seen as effective against only three serotypes.

The vaccine also seems to protect older children aged 12-14 years more (75 per cent efficacy) than younger children aged 2-5 years (34 per cent efficacy). The discrepancy might be because the vaccine works better on children with prior exposure to dengue virus, which is more likely among older children than younger ones.

Another phase 3 trial of the same vaccine is nearing completion in Latin America with more than 20,000 participants aged 9-16 years old, using the same methods as the South-East Asia trial. The results will be published by the end of 2014. Wilder-Smith expects the Latin America trial to report similar results and, due to the larger sample size, more reliable vaccine efficacy with less variation.